Suspension systems are commonly incorporated into structures such as buildings, bridges, and elevated highways, and machinery such as vehicles, to absorb forces and dampen vibrations which might otherwise damage the structure. These suspension systems often incorporate accumulators and one or more springs, such as coil springs (compression or extension), leaf springs, Belleville disc springs, wave springs, cantilever springs, or machined springs. Suspension systems may alternatively include a gas spring, such as an air spring. Conventional air springs typically include an air compressor connected to a bladder. The compression of the air in the bladder is configured to support the weight of the structure and to provide a spring response to loads on the structure.
Conventional suspension systems may also incorporate one or more liquid springs. Some conventional liquid spring systems include a strut connected to a pressure vessel. Some of those systems include a valve between the strut and the pressure vessel. A liquid in the strut is selectively in communication with the pressure vessel via the valve. The valve may be opened to achieve a relatively low spring rate and closed to achieve a relatively higher spring rate of the suspension system. The spring rate of conventional liquid spring systems is also a function of the compressibility of the liquid in the system. Accordingly, the liquid in conventional liquid spring systems is a compressible liquid.
Conventional pressure vessels are designed to minimize or eliminate their expansion by fabricating the pressure vessel out of rigid materials (e.g., steel or certain composites) and/or by incorporating bracketry or other structural elements designed to fix the size of the pressure vessel. Thus, conventional pressure vessels are not intended to be expandable. They are specifically designed not to be expandable, and therefore expansion would be contrary and inconsistent with their purpose.